1. Field of the Invention
This invention relates generally to machines and methods for forming metal panels for constructing metal buildings, and more particularly relates to apparatus and methods for forming curved building panels from flat sheet metal material by crimping.
2. Background and Prior Art
It is known in the prior art to construct metal buildings from metal panels which are arched or curved, assembled side-by-side and seamed together. See U.S. Pat. No. 3,902,288 to Knudson. In such buildings the roof panels continue as the side walls of the building and the basic building construction is in the shape of a self-supporting continuous arch or semicircle when viewed from one end. A machine for making the building panels in which U-shaped panels are corrugated or crimped both on the bottom or "belly" and on the sides to create the curvature is shown in U.S. Pat. No. 3,842,647 to Knudson.
An arched building construction in which the walls and roof are completely arched has advantages, but also has a number of limitations. One limitation is the absence of vertical walls which limits the use of vertical space. Users of metal buildings often want vertical walls both for aesthetic purposes as well as to obtain the use of more vertical space near the edges of the building. The basic size and strength of such metal buildings is also limited by wind and live load limitations as established by local and national building codes. A completely arched building must be limited in size in order to prevent overloading as could occur from extensive wind loads produced by hurricanes. However, when the total roof height is reduced to approximately one-fifth of the total building width, hurricane force winds do not affect the building as much because of the reduced frontal area.
Improvements to the above technology are disclosed in U.S. Pat. Nos. 5,249,445 and 5,359,871 to Morello, incorporated by reference herein in their entirety. These patents disclose microprocessor-controlled methods and apparatus wherein metal building panels could be formed by automatically controlling the radius of curvature and wherein the panels may have a straight as well as a curved portion so that metal panel buildings could be constructed with arched roofs and vertical walls. The cited Morello patents disclose the use of hydraulics and microprocessor controlled machinery which forms U-shaped building panels of predetermined length from a coil of sheet metal. The formed panels are then continuously crimped on their side edges for strength and are adjustably curved by crimping the belly of the panel. The crimping is automatically controlled so that building panels may be formed with vertical wall portions and curved or arched roof portions.
A problem in the prior art, however, was the fact that the depth of the crimp on the side edges of the panel remained constant, even as the radius of the panel being curved changed. If the radius of the panel was tight, and the depth of side crimp was shallow, the side walls of the panel buckled due to the excess material not taken up by the crimp. Analogously, if the radius was large or the panel section being formed was straight, and the depth of side crimp was deep, the belly of the panel buckled due to excess material in the belly not taken up by the crimping. Because of the physical distance between the side crimping apparatus and the main crimping apparatus, the simultaneous adjustment of the side and main crimping apparatus caused the length of panel between the side crimper and the main crimper during this adjustment not to have the change in depth of crimp on the side walls, which caused the buckling effect discussed above. Thus, there exists a need in the art for improvement to such apparatus and methods to eliminate the deleterious buckling effects caused by adjustment of the crimping mechanisms during formation of such panels.